#include <iostream>
#include <cmath>
using namespace std;
int main()
{
   float x1,x2,y1,y2;
   while (cin>>x1>>y1>>x2>>y2)
   {
      printf("%.2f\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
   }
   return 0;
}
